'V' block universal tube vise jaws
grabcad
I printed two of these with PLA and 100% infill, and they can be used to hold tubes in vices. They're useful for bicycle frame building and servicing items like dropper posts. I'm not entirely sure what the minimum and maximum tube diameter is that these tube vice jaws can handle, but they should work for most bike frame tube sizes. Here's a link to the CAD design on Onshape: https://cad.onshape.com/documents/235e7f3a2ca207eabc909dfb/w/a5dbb67fd00d225f0c78c1ff/e/36239f3fb65d77f07da5ccf8. Be aware that I haven't used these much, so let me know if you print them and if they work for you.
With this file you will be able to print 'V' block universal tube vise jaws with your 3D printer. Click on the button and save the file on your computer to work, edit or customize your design. You can also find more 3D designs for printers on 'V' block universal tube vise jaws.